This invention relates in general to sensors and in particular to a method for testing the operation of sensors.
Vehicle control systems utilize a variety of sensors that monitor vehicle operational parameters. Additionally, vehicle electronically controlled brake systems are becoming increasing sophisticated to include the capability to correct vehicle directional movement upon detection of an undesired vehicle motion, such as, for example, loss of directional control on a low mu surface or potential vehicle roll over. Such detection typically involves motion sensors, to include accelerometers and/or angular rate sensors and also usually includes input from other vehicle operating parameter sensors, such as, for example, wheel speed sensors and a steering angle sensor. Vehicle brake control systems typically include an Electronic Control Unit (ECU) that receives the various sensor output signals. A microprocessor within the ECU that is controlled by a stored algorithm monitors the received sensor signals. The microprocessor is operative, upon detection of a potential vehicle directional stability problem, to selectively apply the vehicle brakes and/or vary engine torque to correct the problem.
The motion sensors utilized by the brake control system are also becoming increasingly miniaturized and sophisticated to include signal conditioning circuits. Multiple motion sensors with associated signal conditioning circuits for the sensor outputs may be included on a single sensor chip. The signal conditioning circuits also may include a self testing capacity for monitoring the sensor output signal to detect a malfunctioning sensor. Typically, the self test is carried out during initial vehicle start-up and will generate an error code if the signal conditioning circuit determines that the sensor output signal exceeds a predetermined threshold. Also, upon detecting a malfunctioning sensor, the self test capability may disable the sensor output so an erroneous signal is not sent to the ECU.
However, because vehicles are operated for increasingly lengthy periods of time, limiting self-testing to initial vehicle start-up has effectively increased the operational time of motion sensors between self tests. As a result, if motion sensors begin to malfunction during vehicle operation, the problem may not be detected in a timely fashion. Accordingly, it would be desirable to provide a periodic self test method for the motion sensors that would occur while the vehicle is in operation. Such testing would also be desirable for other sensors utilized by a motor vehicle.